Give the domain of `(x) = (x+9)/(4x^2+39x+27)` using interval notation

The domain of `r(x)` is:   

Box 1: Enter your answer using interval notation. Example: [2,5)
Use U for union to combine intervals. Example: (-oo,2] U [4,oo)
Enter each value as a reduced fraction (like 5/3, not 10/6) or as an integer (like 4 or -2)
Do not enter mixed numbers
Enter DNE for an empty set. Use oo to enter Infinity.